One of the most compelling characters on the show. When viewers were first introduced to Mrs. McDreamy, she was the villain, arriving in the Emerald City just in time to ruin Meredith's relationship with her husband. It turns out that Derek left New York for Seattle after catching her in bed with Mark, a plastic surgeon and his best friend -- a fact he conveniently withheld from Meredith.

While she gave Derek the chance to sign divorce papers and end things between them for good, he declined. They have slowly begun to patch things up, although much guilt and resentment remains. The reappearance of Mark, who tried to lure her back to New York, did not help matters. Addison also hates living in Derek's trailer, and the fact that he adopted Meredith's dog.

Addison specializes in surgery involving extremely young children, including those still in the womb. She has become a mentor to Izzie, and a commanding presence throughout the traditionally male-dominated hospital.